The art of membrane separation devices, particularly those using cartridges having membranes which are spirally wound about central porous tubes, is well-developed today. Such cartridges are used in many and varied separation devices and processes. U.S. Pat. Nos. 3,417,870 and 3,966,616 are examples of patents which show such semipermeable membrane spirally wound cartridges. Such spirally wound membrane cartridges generally employ a central porous collection tube, having a series of holes which provide for fluid flow between the interior and exterior surfaces of the tube. Spirally wound about the exterior surface of this central tube is at least one generally flat tubular envelope usually made of two sheets of adhesively joined semipermeable membane, the interior of which envelope contains spacer or permeate passageway material. A sheet of spacer or inlet flow-passageway-providing material also lies adjacent an outer surface of the envelope and is spirally wound with it about the central tube so as to provide a passageway in the annular region surrounding the tube which extends axially from end to end throughout the spirally wound assembly.
Generally, more than one set of such combinations of tubular envelopes and spacer sheets make up the spiral winding, and the exterior of the wound assembly is usually wrapped in some manner. For example, U.S. Pat. No. 4,600,512 shows a spirally wound assembly in which the wrapped membrane assembly is held together by helical taping about the complete outer cylindrical surface thereof, and such taping can extend to locations along the outer circumferences of molded plastic circular retainers which are located at each end. The particular cartridge shown in this patent is designed to be positioned in a surrounding pressure vessel and aligned therein so as to leave an annular gap between the interior pressure vessel wall and the exterior of the cartridge which serves as a flow passageway for the inlet fluid stream being treated. Other membrane cartridges are designed to fit snugly against the interior surface of a pressure vessel, such as that shown in U.S. Pat. No. 4,548,714, or to fit fairly closely thereto and have an O-ring or chevron-type seal or the like at the inlet end, such as that which is somewhat schematically shown in U.S. Pat. No. 4,517,085.
These spirally wound cartridges are generally manually or semi-automatically wrapped about the central tube, and their exterior surfaces inherently have some undulations, the number of which increases with the number of separate leaves employed in the spiral winding. Moreover, the wrapping procedure is frequently relatively labor-intensive and often requires careful quality control procedures. Thus, improvements in the construction of spirally wound semipermeable membrane cartridges continue to be sought, along with improved methods for making such cartridges.